There is an ongoing search in the textiles field for high strength nonwoven materials. In particular, there is a growing need in the art for nonwoven materials comprising microfibers and/or nanofibers.
Fabrics composed of micro- or nanofibers offer small pore size and large surface area. Thus, they generally bring value to applications where such properties as sound and temperature insulation, fluid holding capacity, softness, durability, luster, barrier property enhancement, and filtration performance are needed. In particular, products intended for liquid and aerosol filtration, composite materials for protective gear and clothing, and high performance wipes could benefit greatly from the introduction of such small fibers.
Manufacturing techniques associated with the production of polymeric micro- and nanofibers are electrospinning, meltblowing, and the use of multicomponent fibers, such as segmented pie and islands-in-the-sea (I/S) fibers. In electrospinning, a fiber is drawn from a polymer solution or melt by electrostatic forces. This process is able to produce filaments with diameters in the range from 40 to 2000 nm. Meltblowing processes are capable of producing fibers having diameters of 0.5 μm to 10 μm. Even though filaments measuring 0.5 μm can be obtained via this technique, most commercially available meltblown media are generally about 2 microns and above.
In general, meltblowing and electrospinning produce nonwoven mats rather than single fibers and these mats consist of fibers characterized by low strength. Thus, electrospun or meltblown fiber webs are typically laid over a suitable substrate that provides appropriate mechanical properties and complementary functionality to the fabric. Moreover, existing meltblowing processes are not able to produce nanofiber webs easily, and they can process only a limited number of polymers. Electrospinning, on the other hand, is able to make nanofiber mats with substantially smaller fibers than meltblown or spunbonded webs; however, this process has very low productivity.
With multicomponent fibers, the I/S approach can produce significantly smaller fibers than the segmented pie technique, however the sea in the I/S fibers has to be removed, and this often creates an environmental issue. Also, since virtually all spunbonds are thermally bonded, subsequent removal of the sea component from thermally bonded substrates generally results in the loss of structure as a result of disintegration of the bond spots. In other words, the art has heretofore failed to provide methods for producing I/S spunbond webs that provide high strength and retain integrity after removal of the sea component. Thus, I/S spunbond webs require an alternative means of bonding the structure in place of thermal bonding.
Because of the above mentioned shortcomings, there are no commercial products available today based on the spunbond I/S technology. The present invention fills such void in the market for the production of large volumes of micro- and nanofiber webs.